Method and apparatus for controlling lights and other devices

ABSTRACT

A dimmer for dimming gas discharge and incandescent lamps can be installed in place of a standard wall-mounted light switch and connected to existing wiring. The dimmer has a switch coupling one or more full wave bridge rectifiers to a main AC source and to existing power wires running through the wall to the fixture. The bridge rectifiers are controlled by the dimming switch such that either the normal AC source waveform is transmitted over the power wires, or a full wave positively or negatively rectified AC waveform is transmitted, or else no voltage is transmitted. At the fixture, the transmitted power waveform is applied to the lamp power terminal of the lamp or ballast as well as to a decoder. A dimming interface receives the decoder output and appropriately adjusts lamp brightness by changing the operating conditions of the lamp in accordance with this output. The dimmer may also be used to control general household devices containing a front-end full wave bridge rectifier.

FIELD OF THE INVENTION

The present invention relates generally to device control circuitry. Ina particular embodiment it relates to a dimmer for use with gasdischarge lamp ballasts and incandescent lamps.

BACKGROUND OF THE INVENTION

Dimming circuits for incandescent lamps are well-known and extensivelyused. However, there are fewer commercially available dimming circuitssuitable for use with gas discharge lamps, such as fluorescent lamps.Available gas-discharge lamp dimming circuits contain complex circuitryand a high number of components which makes them expensive to build,install and retrofit to existing ballasts. Consequently, mostresidential and commercial fluorescent installations do not have dimmingcapability.

Dimming of fluorescent and other gas discharge lamps is commonlyaccomplished by a dimming circuit located in the ballast and controlledusing the well known "0 to 10V" signalling protocol. This protocol usesa pair of dedicated wires to send a dimming control signal representedby a voltage signal of value between 0 and 10 volts to the ballastdimming circuitry. The ballast dimming circuitry then converts thiscontrol signal into a signal adapted to change ballast operatingconditions. While this dimming method is popular for dimming fluorescentand other gas discharge lamps, it suffers from several significantdisadvantages.

In order to provide dimming for existing lighting installations, thededicated wires of this signalling system must be installed withinceilings and walls, resulting in significant installation costs.Further, since each ballast requires a separate set of wires, thelighting system is complex to wire and can pose a safety threat if anyof the wires are improperly installed (i.e., if the dimming signal wiresare mistakenly connected to the main power source, the ballast willshort, severely damaging the device and possibly injuring theinstaller).

Further, signal wires from one ballast must be galvanically isolatedfrom possible interference and noise produced by other ballast signalwires. Such isolation may require the use of additional components whichsignificantly adds to the expense and complexity of a lighting systemcomprising a number of ballasts. Moreover, since the main power wiresare often in close proximity to the signal wires, control signals arestill often affected by electrical interference and noise. Corruptedcontrol signals consequently can cause device malfunctions.

A dimming protocol which offers independent fixture addressing is adigital protocol method developed by Tridonic Corporation. This protocoluses signal wires to transmit digital information representing thedesired brightness level (i.e., 128 or 256 levels of brightness) andother information such as the particular address of the target ballastto be dimmed. While this method allows for increased unit flexibilityand better signal wire economy, the system still requires the use ofcomplex decoders within each ballast and stand alone dimming ballastswhich are typically twice as expensive as the existing 0-10 Voltprotocol dimming ballasts. In addition, the digital signal sent to theballasts is susceptible to electrical noise and interference.

Another dimming signalling system is shown in U.S. Pat. No. 4,181,873 toNuver. U.S. Pat. No. 4,181,873 avoids the need for a separate set ofsignal leads to a lamp ballast by encoding a high frequency signal (200KHz to 400 Hz) on an AC line voltage. This signal provides controlinformation which is used to control the gating to a triac for dimming alamp. However, this dimming protocol is rarely used because such RFcommunications are very sensitive to the electrical noise commonly foundon an AC line. Further, this signalling protocol generates what is knownas "RF pollution" which affects radio frequency transmissions and whichviolates FCC Regulations regarding the maximum level of radio frequencyinterference that any industrial or commercial electrical device mayproduce.

Finally, a power line control system is disclosed in U.S. Pat. No.5,614,811 to Sagalovich. U.S. Pat. No. 5,614,811 discloses encodingvoltage pulses within an AC power line voltage at zero crossing pointsof any one-half AC cycle. The voltage pulses act as control signals forany electrical device which is connected to the AC power line through areceiver/control apparatus. While this control system alleviates somedisadvantages associated with RF pollution, the system utilizesrelatively complex transmitter and receiver circuits and still createssome RF pollution.

Thus, there is a need for a dimmer circuit for gas discharge lampballasts and incandescent or halogen lamps, which can be implemented ina cost-effective manner and which facilitates easy and safeinstallation, and which is not susceptible to electrical interference orcorruption, and which meets established FCC radio interference noiseregulations and which can be easily retrofitted to operate withinnon-dimming ballasts.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a controlcircuit for controlling an electrical load having a load input, saidcontrol circuit comprising:

(a) a power input for receiving an input AC waveform having a selectedRMS value.

(b) a rectifying circuit coupled to said input for producing at a poweroutput one of a plurality of output waveforms from said AC inputwaveform, each output waveform having an RMS value substantially thesame as said selected RMS value,

(c) a controller coupled to said rectifying circuit and operative tocause said rectifying circuit to produce at said power output a selectedone of said output waveforms,

(d) said load input being adapted to be coupled to said power output forreceiving said selected output waveform so that said selected outputwaveform provides power to said load,

(e) and a decoder control circuit adapted to be coupled to said poweroutput and to said load and responsive to the selected output from saidrectifying circuit for controlling said load.

In a second aspect, the present invention provides a method forcontrolling an electrical load at a first location connected by powerwires to an AC source at a second location, said AC source providing anAC waveform having a selected RMS value, said method comprising:

(a) controlling said AC waveform at said second location to produce aset of power waveforms each having an RMS value substantially equal tosaid selected RMS value,

(b) selectively transmitting one of said set of power waveforms fromsaid second location over said power lines to said electrical load toprovide power to said load,

(c) at said first location, decoding said power waveforms andcontrolling said electrical device in accordance therewith.

Further objects and advantages of the invention will appear from thefollowing description, taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram view of a lamp with a universal dimmerconnected thereto, according to the present invention;

FIG. 2 is a schematic diagram of a dimmer switch according to thepresent invention;

FIG. 3a is a waveform diagram of the voltage at the output of the dimmerswitch when neither switch SW₁ nor SW₂ of FIG. 2 is depressed;

FIG. 3b is a waveform diagram of the voltage at the output of the dimmerswitch when switch SW₁ of FIG. 2 is depressed;

FIG. 3c is a waveform diagram of the voltage at the output of the dimmerswitch when switch SW₂ of FIG. 2 is depressed;

FIG. 3d is a waveform diagram of the voltage at the output of the dimmerswitch when both switches SW₁ and SW₂ of FIG. 2 are depressed;

FIG. 4 is a schematic of a simple decoder according to the presentinvention;

FIG. 5a is a waveform diagram of the voltage across C_(D) of FIG. 4 whenneither switch SW₁ or SW₂ of FIG. 2 is depressed;

FIG. 5b is a waveform diagram of the voltage across C_(D) of FIG. 4 whenswitch SW₁ of FIG. 2 is depressed;

FIG. 5c is a waveform diagram of the voltage across C_(D) of FIG. 4 whenswitch SW₂ of FIG. 2 is depressed;

FIG. 5d is a waveform diagram of the voltage across C_(D) of FIG. 4 whenboth switches SW₁ and SW₂ of FIG. 2 are depressed;

FIG. 6a shows a typical load control for use with a typical incandescentlamp;

FIG. 6b shows a typical load control for use with a typical gasdischarge lamp ballast;

FIG. 7 is a schematic of an alternative dimmer switch according to theinvention;

FIG. 8 is a schematic of another alternative dimmer switch andrectifying stage according to the invention;

FIG. 9 is a block diagram of the FIG. 8 circuit;

FIG. 10 is a diagram showing a modified waveform transmitted by a dimmerswitch and rectifying stage according to the invention;

FIG. 11 is a block diagram showing a modification of the FIG. 9 circuit;

FIG. 12 shows a further modification of the dimmer switch and rectifyingstage of FIG. 2, and

FIG. 13 shows a still further modification of the dimmer switch andrectifying stage of FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is first made to FIG. 1, which shows a universal dimmer 10according to a preferred embodiment of the invention. Dimmer 10 includesa dimmer switch 12, a rectifying stage 14, a decoder 16 and a loadcontrol 18.

Dimmer switch 12 has input terminals AC₁, and AC₂ connected to an ACsource 20, typically a 60 Hz power line from a distribution panel, andis typically mounted in a conventional wall switch box. Dimmer switch 12is designed to replace a standard wall-mounted light switch and isattached to existing wiring. Dimmer switch 12 includes manual orelectronic switches SW₁ and SW₂ which together can form four differentswitch configurations. Dimmer switch 12 has output terminals AC₃, AC₄connected through existing power wires 22 to decoder 16 located in alighting fixture 24.

Rectifying stage 14 is connected to (and forms part of) dimmer switch 12and is typically contained in a box-like housing on the back side ofdimmer switch 12. Rectifying stage 14 includes two full wave bridgerectifiers BR₁ and BR₂. Various configurations of switches SW₁ and SW₂result in the connection of the inputs of neither, one, or both ofbridge rectifiers BR₁ and BR₂ to AC source 20. Various configurations ofswitches SW₁ and SW₂ also result in the connection of the outputs ofneither, one or both bridge rectifiers BR₁ and BR₂ to power wires 22.

When the inputs of bridge rectifier BR₁ (or BR₂) are connected to ACsource 20 and the outputs of bridge rectifier BR₁ (or BR₂) are connectedto power wires 22, bridge rectifier BR₁ (or BR₂) becomes active andproduces a full wave rectified AC signal on its output. Bridge rectifierBR₁ is configured within rectifying stage 14 such that when bridgerectifier BR₁ is active, it will conduct and provide a full wavenegatively rectified AC signal at terminals AC₃, AC₄ to decoder 16.Similarly, an active bridge rectifier BR₂ will provide a full wavepositively rectified AC signal to decoder 16.

When both bridge rectifiers BR₁ and BR₂ are inactive, an AC signal fromAC source 20 is transmitted directly through dimmer switch 12 viaterminals AC₃, AC₄ to power wires 22, as will be explained. When bridgerectifiers BR₁ and BR₂ are both active, a zero voltage signal is outputto decoder 16, as will also be explained. In this way, four differentpower waveforms may be produced by rectifying stage 14 for output atterminals AC₃, AC₄ to decoder 16 in accordance with the four differentpossible configurations of switches SW₁ and SW₂.

Decoder 16 is installed within fixture 24 and is connected to dimmerswitch 12 through power wires 22. Power wires 22 are also connected to alamp power terminal 26, which (through one or two wires, depending onthe type of lamp) provides operational power to a lamp 28. Decoder 16receives one of the four possible power waveforms from dimmer switch 12through power wires 22. If dimmer 10 is used in association with a lampthat utilizes a ballast, then decoder 16 may be specifically installedwithin that ballast (not shown) in fixture 24. For application to anincandescent or halogen lamp, decoder 16 can be simply installed at aconvenient location within fixture 24. The power waveform is appliedacross a resistor R_(D) and a capacitor C_(D) of decoder 16. The voltageacross capacitor C_(D), V_(D) is then applied to load control 18. Theoutput of decoder 16 will be either a fixed positive, fixed negative orzero value as will be further described.

Load control 18 includes a simple dimming control circuit to adjust theoutput of a ballast or the brightness level of a lamp, in accordancewith the value of the output voltage of decoder 16. Load control 18 canbe used to adapt dimmer 10 for use with a gas discharge lamp, such asfluorescent, high intensity discharge and others associated with anytype of ballast, including conventional non-dimming ballasts.Alternatively, load control 18 can adapt dimmer 10 for use directly witha non-ballast type lamp, such as an incandescent (which includeshalogen) lamp.

FIG. 2 shows an electrical schematic of dimmer switch 12, illustratingthe interconnections between switches SW₁ and SW₂ and bridge rectifiersBR₁ and BR₂ such that four different power waveforms are output todecoder 16, each corresponding to one of four possible configurations ofswitches SW₁ and SW₂.

Switches SW₁ and SW₂ each have four mechanically connected subswitchesSW₁₁, SW₁₂, SW₁₃ and SW₁₄, and SW₂₁, SW₂₂, SW₂₃, and SW₂₄, respectively.Each subswitch has two possible configurations. Contact 2 can beconnected either to contact 1 (denoted "(1-2)") or to contact 3 (denoted"(2-3)"). When switch SW₁ is "open" or non-depressed, all of themechanical contacts will have configuration (1-2). When switch SW₁ is"closed" or depressed, all of the mechanical contacts will haveconfiguration (2-3).

Bridge rectifier circuits BR₁ and BR₂ are conventional and each has fourdiodes D1, D2, D3 and D4 and D5, D6, D7 and D8, connected in series,respectively. AC source 20 can be connected to bridge rectifier BR₁through terminals A and B and non-depressed switch SW₂. Similarly, ACsource 20 can be connected to bridge rectifier BR₂ through terminals A'and B' and non-depressed switch SW₁. Bridge rectifier BR₁ can beconnected to terminals AC₃ and AC₄ (and thus to decoder 16 and lamppower terminal 26) through terminals C and D and depressed switch SW₁.Bridge rectifier BR₂ can be connected to terminals AC₃ and AC₄ throughterminals C' and D' and depressed switch SW₂. When bridge rectifier BR₁(or BR₂) is connected to both AC source 20 and terminals AC₃ and AC₄, afull wave rectified AC signal will appear on terminals C and D (or C'and D').

When both switches SW₁ and SW₂ are "open" or non-depressed, AC source 20is connected to bridge rectifiers BR₁ and BR₂ via subswitch contactsSW₁₃ (1-2), SW₁₄ (1-2), SW₂₃ (1-2) and SW₂₄ (1-2). However, sinceneither bridge rectifier BR₁ nor BR₂ is connected to the rest of dimmer10 circuit, bridge rectifiers BR₁ and BR₂ are inactive. Accordingly, anunmodified AC signal will flow directly from terminals AC₁ and AC₂,through subswitch contacts SW₁₁ (1-2), SW₁₂ (1-2), SW₂₁ (1-2) and SW₂₂(1-2) and through terminals AC₃ and AC₄ to decoder 16 and lamp powerterminal 26. The resulting voltage waveform V_(OUT) across terminals AC₃and AC₄ is shown in FIG. 3a and is the same as the input waveform fromsource 20.

When switch SW₁ is depressed and SW₂ is non-depressed, AC source 20 isdisconnected from the input of bridge BR₂ by the subswitch contact SW₁₃(2-3) and SW₁₄ (2-3). The direct AC connection from AC source 20 toterminals AC₃ and AC₄ is also severed by subswitch contacts SW₁₁ (2-3)and SW₁₂ (2-3). Further, terminals C and D of bridge rectifier BR₁ areconnected to terminals AC₃ and AC₄ through subswitch contacts SW₁₁ (2-3)and SW₁₂ (2-3), respectively such that bridge rectifier BR₁ is nowactive and producing a full wave negatively rectified AC signal, withpositive polarity (at terminal C) being connected to terminal AC₄ andnegative polarity (at terminal D) being connected to terminal AC₃. Theresulting voltage V_(OUT) is shown in FIG. 3b.

When switch SW₁ is non-depressed and SW₂ is depressed, the AC input ofbridge BR₁ is disconnected from the AC line by the subswitch contactsSW₂₃ (2-3) and SW₂₄ (2-3) and the direct AC connection between AC source20 and terminals AC₃ and AC₄ is severed by subswitch contacts SW₂₁ (2-3)and SW₂₂ (2-3). Further, terminals C' and D' of bridge rectifier BR₂ areconnected to terminals AC₃ and AC₄ through subswitch contacts SW₂₁ (2-3)and SW₂₂ (2-3) respectively such that bridge rectifier BR₂ is active andproduces a full wave positively rectified AC signal with positivepolarity (at terminal C) being connected to AC₃ and negative polarity(at terminal D) being connected to AC₄. The resulting voltage V_(OUT) isshown in FIG. 3c.

When both switches SW₁ and SW₂ are depressed, the direct AC connectionis severed by both sets of "closed" subswitch contacts SW₁₁ (2-3), SW₁₂(2-3), SW₂₁ (2-3) and SW₂₂ (2-3). Further, both sets of terminals C andD and C' and D' of bridge rectifiers BR₁ and BR₂ are connected toterminals AC₃ and AC₄ through subswitch contacts SW₁₂ (2-3), SW₁₁ (2-3),SW₂₁ (2-3) and SW₂₂ (2-3) respectively, such that both bridge rectifiersBR₁ and BR₂ are active. Since bridge rectifiers BR₁ and BR₂ each producerectified AC signals with opposite polarities, zero voltage consequentlyresults across terminals AC₃ and AC₄ as shown in FIG. 3d.

Since switches SW₁ and SW₂ can be configured such that the full ACsignal can pass directly through the device for full lamp operation oralternatively, such that no voltage is applied to the lamp, dimmer 10also replaces the on/off functionality of a lamp switch.

Once switches SW₁ and SW₂ are returned to their normal non-depressedpositions, the unmodified AC power again flows directly from terminalsAC₁ and AC₂ through subswitch contacts SW₁₁ (1-2), SW₁₂ (1-2), SW₂₁(1-2) and SW₂₂ (1-2) to power wires 22 through terminals AC₃ and AC₄,with voltage V_(OUT) as shown in FIG. 3a. It will be seen that in FIGS.3a, 3b and 3c, the RMS value of each half cycle of the waveform is inall cases the same (or substantially the same).

In this way, rectifying stage 14 can produce four different powerwaveforms for transmission over power wires 22 each corresponding to oneof the four possible configurations of switches SW₁ and SW₂. Aspreviously discussed, either one or both power wires 22 which areconnected to decoder 16 are also connected to lamp power terminal 26(depending on the type of lamp, and as discussed in connection withFIGS. 6a, 6b). It should be noted that when full wave positively ornegatively rectified AC signals are provided to lamp power terminal 26of incandescent lamps or gas discharge lamp ballasts, these devices willcontinue to operate in a normal fashion.

Specifically, incandescent lamps are normally directly connected to ACvoltage and operate based on the V_(rms) of the AC signal received.Since the RMS value of each half cycle of a full wave positively ornegatively rectified AC signal is the same as the RMS value of each halfcylce of an unmodified or full wave AC signal, an incandescent lamp willnot differentiate between a full wave AC signal or a full wavepositively or negatively AC rectified signal. The rectifying stage 14 isthus "transparent" to a load which consists of an incandescent lamp,i.e. the load will not notice the changes in waveform, but the changesin waveform can be used for signalling and hence control, withoutcreating RF pollution and without being particularly susceptible tonoise.

Ballasts for gas discharge lamps all include a full wave bridgerectifier at the front end of their circuits for rectifying an incomingAC signal. This front end internal bridge rectifier will rectify a fullwave positively or negatively rectified AC signal just as itconventionally does a normal full wave AC signal to produce a full wavepositively rectified AC signal. As a result, typical ballasts willcontinue to operate normally regardless of whether the input voltagesignal is a normal full wave AC signal, or a full wave positively ornegatively rectified AC signal. The rectifying stage 14 is thereforealso "transparent" to a gas discharge lamp ballast, i.e. the ballastalso will not notice the changes in waveform, yet the changes inwaveform can be used as indicated above.

FIG. 4 shows a simple decoder 16 which comprises capacitor C_(D),resistor R_(D), and two optocouplers OC_(D1) and OC_(D2). Decoder 16receives voltage signal V_(OUT) from dimmer switch 12 (not shown in FIG.4) at terminals AC₃ and AC₄ and outputs a dimming control signal atterminals LAMP₁ and LAMP₂ to dimming interface 18 (not shown in FIG. 4).For simplicity, power supply arrangements to the optocouplers are notshown in FIG. 4 but are well known.

Capacitor C_(D) and resistor R_(D) are connected in series, with theircomponent values chosen such that the resulting time constant (RC) islonger than the duration of one half of the regular AC signal cycle.This ensures that when the unmodified AC signal shown in FIG. 3a isapplied across terminals AC₃ and AC₄, capacitor C_(D) will not be ableto accumulate sufficient charge to activate optocouplers OC_(D1) andOC_(D2) as will be explained. Although other values and device types canbe chosen, capacitor C_(D) may be a 16 Volt electrolytic capacitor ofvalue 220 μF and resistor R_(D) may have a value of 10 KΩ. While,application of the regular AC signal of FIG. 3a will not causeoptocouplers OC_(D1) and OC_(D2) to conduct, application of the fullwave negatively or positively rectified voltage of FIG. 3b or 3c, willcause capacitor C_(D) to commence charging until either optocouplerOC_(D1) or OC_(D2) starts to conduct, as will be explained.

Conventional optocouplers OC_(D1) and OC_(D2) are used within decoder 16to provide isolation between decoder 16 and device interface 18.Specifically, optocouplers OC_(D1) and OC_(D2) each contain a LED and aphototransistor detector. When current flows through optocoupler OC_(D1)or OC_(D2), light is emitted by the LED. The light is received by thephototransistor detector and the amount of light received determines theamount of current allowed to pass from the collector to the emitter ofthe phototransistor detector. While other voltage rated optocouplers maybe chosen, optocouplers OC_(D1) and OC_(D2) may become operational uponapplication of a voltage of approximately 1.3 Volts across theirrespective LEDs.

When both switches SW₁ and SW₂ are non-depressed, an AC signal will beapplied across terminals AC₃ and AC₄, as previously discussed. Since theresulting time constant (RC) is chosen to be approximately 2.2 secondsand since each half AC cycle has a duration of 16.7 milliseconds,voltage V_(D) will never reach + or -1.3 Volts required to activate theLED of optocoupler OC_(D1) or OC_(D2). Specifically, with preferredvalues, voltage V_(D) will be either +0.91 or -0.91 Volts, depending onthe polarity of the half cycle. Thus, when a regular AC signal isapplied across terminals AC₃ and AC₄, voltage V_(D) will consist of anAC signal with amplitude 0.91 Volts as shown in FIG. 5a. Accordingly,neither optocoupler OC_(D1) nor OC_(D2) will conduct, since voltageV_(D) will not be sufficient to ignite the LED of optocoupler OC_(D1) orOC_(D2), and accordingly, load control 18 will not be triggered.

When switch SW₁ is depressed, dimming switch 12 provides a rectified ACsignal with negative polarity at terminal AC₃ and positive polarity atterminal AC₄ as previously described. Accordingly, current will flowinto capacitor C_(D) from terminal AC₃ and AC₄ and capacitor C_(D) willcommence charging. Capacitor C_(D) will charge to -1.3 Volts within 23.8milliseconds as shown in FIG. 5b. When voltage V_(D) reaches -1.3 Volts,the LED of optocoupler OC_(D2) will ignite and cause the transistor ofOC_(D2) to open and provide voltage V_(D) to terminal LAMP₂. Since thecharging time is 23.8 milliseconds, when a user presses switch SW₁,optocoupler OC_(D2) will start conducting before the user can physicallyrelease switch SW₁ to ensure operational reliability.

As long as switch SW₁ remains depressed, capacitor C_(D) will remaincharged such that voltage V_(D) is -1.3 Volts. Once SW₁ is released,C_(D) will start discharging into the LED circuit and V_(D) will fallbelow the voltage required to activate optocoupler OC_(D2).Consequently, the transistor of optocoupler OC_(D2) will close and novoltage will appear across terminals LAMP₁ and LAMP₂.

When switch SW₂ is depressed and switch SW₁ is non-depressed, dimmingcontrol 12 provides a full wave positively rectified AC signal withpositive polarity at terminal AC₃ and negative polarity at terminal AC₄.Accordingly, current will flow into capacitor C_(D) from terminal AC₃ toAC₄ and capacitor C_(D) will commence charging. Voltage V_(D) willaccordingly rise to the value of +1.3 Volts within 23.8 milliseconds inan analogous manner as described above, as shown in FIG. 5c. Whenvoltage V_(D) reaches +1.3 Volts, the LED of optocoupler OC_(D1) will beignited and the transistor of OC_(D1) will open and provide voltageV_(D) to terminal LAMP₁. Again, since voltage V_(D) reaches +1.3 Voltswithin 23.8 milliseconds, optocoupler OC_(D1) will start conductingbefore the user can physically release switch SW₂ to ensure operationalreliability.

As long as switch SW₂ is held, capacitor C_(D) will remain charged withvoltage V_(D) being +1.3 Volts. Again, once SW₂ is released, C_(D) willstart discharging into the LED circuit and V_(D) will drop below thevoltage required to activate optocoupler OC_(D1). Consequently, thetransistor of optocoupler OC_(D1) will close and zero voltage willappear across terminals LAMP₁ and LAMP₂.

When both switches SW₁ and SW₂ are depressed, dimming control 12provides zero voltage across terminals AC₃ and AC₄ as previouslydescribed. Accordingly, no current will flow into capacitor C_(D), V_(D)will be zero (as shown in FIG. 5d) and no voltage will appear acrossterminals LAMP₁ and LAMP₂.

In this manner, either +1.3 V, -1.3 V or 0 V DC, will be applied acrossterminals LAMP₁ and LAMP₂ for input into dimming interface or loadcontrol 18.

FIG. 6a shows an exemplary load control 18a for use in association withan incandescent lamp 28. Load control 18a comprises a microcontroller40, timer circuit 42 and a triac Q₁₀. It should be noted that while asimple dimming method for incandescent lamps has been chosen forillustrative purposes, load control 18 may be adapted to incorporatevarious other known incandescent dimming circuitry.

Microcontroller 40 may be any commercially available programmable devicesuch as a Motorola 6800 microcontroller, although it should beunderstood that any type of logic circuit with similar operatingfunctions can be utilized. Storage of program instructions and otherstatic data is provided by a read only memory (ROM) 44, while storage ofdynamic data is provided by a random access memory (RAM) 46. Both memoryunits 44 and 46 are controlled and accessed by microcontroller 40.

Timer 42 is a widely used Model 555 timer which utilizes an RCoscillator to produce a constant timing frequency signal. An appliedreference signal produces a first polarity output. An opposite polarityoutput is produced at a time thereafter determined by an applied DClevel.

Triac Q₁₀ is a conventionally bidirectional thyristor or a triac. Itshould be understood that triac Q₁₀ could be any other type ofsemiconductor switching element, such as a single thyristor or twothyristors arranged in anti-parallel configuration. Triac Q₁₀ isconnected in series with lamp 28 to control the application of powerfrom lamp power terminal 26 to lamp 28 in a known manner. When triac Q₁is fully conducting, a maximum amount (approximately 95%) of currentflows through lamp 28. When triac Q₁₀ is not conducting, a minimumamount of current (approximately 5%) flows through lamp 28. Bycontrolling the period of conduction of triac Q₁₀, the current throughlamp 28 can be varied between the dim and full lamp current values.

Microcontroller 40 is connected to terminals LAMP₁ and LAMP₂ andoperates in accordance with the voltage present across these terminals.Microcontroller 40 uses timer circuit 30 to generate a gate signalwhich, when applied to the gate of triac Q₁₀, will affect the time offiring (or the electrical conduction angle) of triac Q₁₀. By controllingthe time of firing of the triac Q₁₀, microcontroller 40 can control thepercentage of time lamp 28 is on, and thus the intensity of lampbrightness.

Microcontroller 40 is programmed to poll the voltage present acrossterminals LAMP₁ and LAMP₂, on a regular basis, such as (e.g.) every 0.5seconds. If this voltage is zero, microcontroller 40 will not change thefrequency of the signal being output to the gate of triac Q₁₀ or thegating signal. However, if microcontroller 40 detects a positive ornegative voltage across terminals LAMP₁ and LAMP₂, microcontroller 40 isprogrammed to increase or decrease, respectively, the frequency of thegating signal in a step-wise manner. Microcontroller 40 continues toincrement the frequency of the gating signal until a zero voltage isdetected across terminals LAMP₁ and LAMP₂ or until a maximum or minimumbrightness is reached. Each increment step has a duration of (e.g.)approximately 1 second to allow the user sufficient time to select theappropriate brightness for lamp 28.

When neither switch SW₁ nor SW₂ is depressed, the voltage present acrossterminals LAMP₁ and LAMP₂ will be zero. Accordingly, microcontroller 40will not change the frequency of the gate signal being applied to thegate of triac Q₁₀ and no change in light intensity will result.

If switch SW₁ is depressed then microcontroller 40 will detect anegative voltage across terminals LAMP₁ and LAMP₂ and will decrease thefrequency of the gating signal until the minimum brightness level isreached, or until the user releases switch SW₁, or until the useradditionally depresses switch SW₂. If the user releases switch SW₁,microcontroller 40 will maintain the gating signal at the attainedfrequency value. This allows a user to dim lamp 28 to a desiredbrightness level by depressing switch SW₁ until that level is reached.If user additionally depresses switch SW₂, then zero power will beprovided through power wires 22, and microcontroller 40 then causes lamp28 to turn off (by shutting off triac Q₁₀).

If switch SW₂ is depressed then microcontroller 40 will detect apositive voltage across terminals LAMP₁ and LAMP₂ and increase thefrequency of the gating signal until the maximum brightness level isreached, or until the user releases switch SW₂, or until the useradditionally depresses switch SW₁. If the user releases switch SW₂,microcontroller 40 will maintain the gating signal at the attainedfrequency value. This allows a user to increase the brightness of lamp28 to a desired level by depressing switch SW₂ until that level isreached. If user additionally depresses switch SW₁, then zero power willbe provided through power wires 22 and lamp 28 will turn off.

FIG. 6b shows an exemplary load control 18b adapted for use with aballast-type gas discharge lamp 28. Load control 18b utilizes amicrocontroller 50 and a timer 52 to change the operating oscillationfrequency or duty cycle of the power of a typical electronic ballast.Microcontroller 50 is of similar specification to microcontroller 40with ROM 51 and RAM 53. It should be noted that although the followingdiscussion relates to the adaptation of a very simple and typicalelectronic ballast, it is possible to adapt the present invention withinany type of lamp ballast by suitably controlling ballast power.

A typical electronic ballast, as is well known, includes a bridgerectifier 54, a boost converter 56, an inverter 58 and a resonancecircuit 60. AC signal 20 is passed through bridge rectifier 54 and intoboost converter 56. Boost converter 56 provides a regulated voltage toinverter 58. Inverter 58 changes the DC voltage to AC voltage at highfrequencies and includes transistors Q₁₁ and Q₁₂ at its output. Thesignal generated by transistors Q₁₁ and Q₁₂ is typically applied toresonance circuit 60. Resonance circuit 60 is directly coupled to lamp28 and is commonly used to avoid the necessity of an output transformer.Dimming is typically achieved by varying the frequency of operation ofinverter 58 by controlling the operation of transistors Q₁₁ and Q₁₂.

Microcontroller 50 and timer 52 are configured to form a voltagecontrolled oscillator which changes the oscillation frequency or dutycycle of ballast power, in response to the voltage across terminalsLAMP₁ and LAMP₂. Specifically, microcontroller 50 provides a variablesquare wave output to drive transistors Q₁₁ and Q₁₂ of inverter 58 tochange the frequency of operation of inverter 58. By varying thefrequency of the square wave output of microcontroller 50, theoperational frequency of inverter 58 is suitably affected.

As previously described, microcontroller 50 regularly polls to check thevoltage present across terminals LAMP₁ and LAMP₂. If this voltage isdetermined to be zero (ie. while both switch SW₁ and SW₂ arenon-depressed), microcontroller 50 will not change the operation ofinverter 58 and no change in light intensity will result.

If switch SW₁ is depressed, then microcontroller 50 will detect anegative voltage across terminals LAMP₁ and LAMP₂ and provide a controlsignal to inverter 58 such that lamp 28 is dimmed until the minimumbrightness level is reached, or until the user releases switch SW₁, oruntil the user additionally depresses switch SW₂. If the user releasesswitch SW₁, microcontroller 50 will maintain the operation of inverter58 at that value. This allows a user to dim lamp 28 to a desiredbrightness level by depressing switch SW₁ until that level is reached.If user additionally depresses switch SW₂, then zero power will beprovided through power wires 22 and lamp 28 will turn off.

If switch SW₂ is depressed then microcontroller 50 will detect apositive voltage across terminals LAMP₁ and LAMP₂ and provide a controlsignal to inverter 58 such that the frequency of the oscillation ofinverter 58 is increased until the maximum brightness level is reached,or until the user releases switch SW₂, or until the user additionallydepresses switch SW₁. If the user releases switch SW₂, microcontroller50 will not change the operation of inverter 58 and no change in lightintensity will result. This allows a user to increase the brightness oflamp 28 to a desired level by depressing switch SW₂ until that level isreached. If user additionally depresses switch SW₁, then zero power willbe provided through power wires 22 and lamp 28 will turn off.

Accordingly, dimmer 10 can be adapted for use with a variety of lampsincluding gas discharge, halogen and incandescent lamps, using theappropriate load control 18a or 18b.

FIG. 7 shows an electronic schematic of an alternative dimmer switch 12and rectifying stage 14. Since simple mechanical connectors can causeload flickering, SCRs and zero-crossing optocouplers are utilized forflicker-free operation. As before, terminals AC₁ and AC₂ connect dimmerswitch 12 to AC source 20 and terminals AC₃ and AC₄ connect dimmingswitch 12 to decoder 16 and to input power terminal 26.

Switches SW₁ and SW₂ of FIG. 2 are implemented using two switches S₁ andS₂ connected to transistors T₉, T₁₀ and T₁₁. Bridge rectifiers BR₁ andBR₂ of FIG. 2 are implemented using SCRs T₂, T₃, T₆, and T₇ and SCRs T₁,T₄, T₅, and T₈, respectively as will be described. All transistors T₉,T₁₀ and T₁₁, SCRs T₁, T₂, T₃, T₄, T₅ T₆, T₇, T₈ and switches S₁ and S₂are powered using a conventional power supply 62 which produces voltageV_(C).

When neither switch SW₁ nor SW₂ is depressed, the base of transistor T₁₁is connected to V_(C) through subswitch contact S₁₃ (1-2) and S₂₃ (1-2)and thus transistor T₁₁ is conductive. Transistor T₁₁ will switch on theLEDs of optocouplers OC₁, OC₂, OC₇ and OC₈ which will switch on SCR'sT₁, T₂, T₃, and T₄ at the zero crossing points of the AC signal presenton terminals AC₁ and AC₂. Accordingly, an AC signal will flow directlyfrom terminals AC₁ and AC₂ to terminals AC₃ and AC₄.

When switch S₁ is depressed and switch S₂ is non-depressed, the base oftransistor T₁₀ is connected to V_(C) through subswitch contact S₁₁ (2-3)and transistor T₁₁ is disconnected from V_(C) by subswitch contact S₁₃(2-3). Accordingly, transistor T₁₀ will conduct and switch onoptocouplers OC₂, OC₃, OC₆ and OC₈ which will switch on SCR's T₂, T₃,T₆, and T₇. SCR's T₂, T₃, T₆, and T₇ form a bridge rectifier (analogousto BR1 of FIG. 2), with an AC signal being input to terminals A and Band a full wave rectified AC signal with positive polarity (at terminalC) being connected to AC₄ and negative polarity (at terminal D) beingconnected to AC₃. The resulting voltage V_(OUT) will be the same as thatshown in FIG. 3b.

When switch S₁ is not depressed and switch S₂ is depressed, the base oftransistor T₉ is connected to voltage V_(D) through subswitch contactS₂₁ (2-3) and base of transistor T₁₀ is disconnected from V_(C) bysubswitch contact S₁₁ (1-2). Accordingly, transistor T₉ will conduct andswitch on optocouplers OC₁, OC₄, OC₅ and OC₇ which will switch on SCR'sT₁, T₄, T₅, and T₈. SCRs T₁, T₄, T₅, and T₈ form a bridge rectifier(analogous to BR2 of FIG. 2), with an AC signal being input to terminalsA and B and a full wave rectified AC signal with positive polarity (atterminal D) being connected to AC₃ and negative polarity (at terminal C)being connected to AC₄. The resulting voltage V_(OUT) which results fromswitch SW₁ being depressed will be the same as that shown in FIG. 3c.

When both switches S₁ and S₂ are depressed, both outputs of bridgerectifiers BR₁ and BR₂ are connected to terminals AC₃ and AC₄ throughsubswitch contacts S₁₁ (2-3), S₁₂ (2-3), S₂₁ (2-3) and S₂₂ (2-3) suchthat both bridge rectifiers BR₁ and BR₂ are active. Since bridgerectifiers BR₁ and BR₂ produce AC signals with opposite polarities, zerovoltage appears across terminals AC₃ and AC₄. The resulting voltageV_(OUT) is the same as that shown in FIG. 3d.

In use, dimmer 10 may be used to dim, brighten, turn on, or turn offlamp 28, by appropriately depressing switches SW₁ and/or SW₂. When lamp28 is off, lamp 28 can be turned on by several switch configurations.For example, microcontroller 40 or 50 may be programmed to toggle lamp28 power alternately on and off when lamp 28 has been off and itsubsequently detects that voltage V_(D) is zero (i.e. both switches SW₁and SW₂ are depressed). Alternatively, microcontroller 40 or 50 may beprogrammed to apply full power to lamp 28 when lamp 28 has been off andsubsequently it detects that either voltage V_(D) is -1.3 Volts or +1.3Volts (i.e. switch SW₁ or SW₂ has been depressed).

Once on, the brightness of lamp 28 can be dimmed by depressing switchSW₁. When switch SW₁ is depressed, dimmer 10 will cause dimming of lamp28 in a step-wise manner until the user determines that an appropriatelighting intensity has been reached and releases switch SW₁. Theintensity of lamp 28 will remain set at this level until the userrequires further dimming or brightening. If increased brightness isdesired, the user depresses switch SW₂, which will cause dimmer 10 toincrease the brightness of lamp 28 in a step-wise manner until thedesired level has been reached and switch SW₂ is released. The user mayturn lamp 28 off at any time by depressing both switches SW₁ and SW₂.

FIG. 8 shows an implementation of dimmer 10 using a microcontroller 70,which may typically be microcontroller PIC 12c 508 supplied by MicrochipTechnology Inc. of Chandler, Ariz., U.S.A. Microcontroller 70 has pin 1connected to a positive supply voltage (not shown), pin 8 connected toground, and pins 6 and 7 connected to pushbutton switches S₁₀ and S₁₁respectively to function as inputs. (Capacitors C₄, C₅ are connectedacross the switches S₁₀, S₁₁ to act as debouncers). Pins 2 to 5inclusive function as outputs. Microcontroller 70 has the operatingcharacteristics that with switches S₁₀, S₁₁ open, pins 2 to 5 inclusiveare normally low. If either switch is pushed, pin 2 goes high. If thepushed switch is released before one second, pin 2 remains high untilfurther action is taken. The remaining outputs stay low. If bothswitches are pushed simultaneously, then all pins become low and staylow. (The reference to "all pins" means the output pins 2 to 5.)

If switch S₁₀ is pushed and held more than one second, then pin 2becomes low, and 12 milliseconds after the time when pin 2 became low,pins 3 and 5 become high and stay high as long as switch S₁₀ remainspushed, but if switch S₁₀ is held in closed position for more than 20seconds, then pins 3 and 5 become low again. The same applies for switchS₁₁, except that after it has been held for more than one second, pins 4and 5 go high and then after 20 seconds go low.

Power to terminal 1 of microcontroller 70 is derived from the AC inputline, by means of diode D₈, zener diode D₇, capacitors C₂ and C₃, andresistor R₁₂. Power for the remainder of the FIG. 8 circuit isprovidedfrom the AC input line via diode D₅, zener diode D₆. andcapacitor C₁.

FIG. 8 will best be understood from a description of its operation,which is as follows. Normally, with neither switch S₁₀ nor switch S₁₁pushed, pins 2, 3, 4 and 5 are all low. AC input terminals AC₁, AC₂ aredisconnected from the output terminals AC₃, AC₄ by triacs T₅₅, T₅₆,which are turned off.

If either switch S₁₀, S₁₁ is touched, and provided that it is touchedonly for a brief instant, pin 2 of microcontroller 70 goes high. Thisswitches on transistor T₅₁, turning on optocouplers OK₆, OK₅ and thusturning on triacs T₅₅, T₅₆. Triacs T₅₅, T₅₆ connect the AC signal atinput terminals AC₁, AC₂ to output terminals AC₃, AC₄, producing anunmodified AC power signal (as shown in FIG. 3a) at terminals AC₃, AC₄(e.g. to operate a lamp at full brightness).

If during AC operation as described above, both switches S₁₀, S₁₁ aretouched at the same time, then all pins of microcontroller 70 go low,switching off all circuitry. This disconnects the AC power from terminalAC₃ and AC₄, in effect turning off the lamp.

If switch S₁₀ is then pushed and held for more than one second, pin 2goes high and then low but 12 milliseconds after pin 2 goes low, pins 3and 5 go high. This turns on transistors T₅₂, T₅₈, thus turning onoptocouplers OK₇, OK₈ and OK₃, OK₂. Optocouplers OK₇, OK₈ turn onthyristors T₅₇, T₅₄ while optocouplers OK₃, OK₂ turn on thyristors Q₅₁,Q₅₃. Thyristors T₅₇, T₅₄ together with diodes D₅₂, D₅₄ form a bridgerectifier (which can be switched on and off by means of the thyristorsT₅₇, T₅₄), producing a full wave rectified negative going outputwaveform (as shown in FIG. 3b) which is connected by Q₅₁, Q₅₃ to outputterminals AC₃, AC₄. This waveform continues until switch S₁₀ isreleased, or after 20 seconds (whichever is first) at which time pins 3,5 go low, switching off the components listed above. The unmodified ACwaveform at output terminals AC₃, AC₄ is then restored.

Similarly, if the user pushes switch S₁₁ for more than one second, pin 2goes high and then low (switching off the normal AC from the outputterminals), and after a 12 millisecond delay (to allow the componentstime to switch off), pins 4, 5 go high. This turns on transistors T₅₃,T₅₈. Transistor T₅₃ turns on optocouplers OK₄, OK₁ which triggersthyristors Q₅₄, Q₅₂. Transistor T₅₈ activates optocouplers OK₇, OK₈ andconsequently thyristors T₅₇, T₅₄. Via thyristors Q₅₂, Q₅₄ this producesa positive going output on terminals AC₄ with respect to AC₃, as shownin FIG. 3c.

It will be seen that in the FIG. 8 arrangement, only one bridge is used(T₅₇, T₅₄, D₅₂, D₅₄). This bridge can be switched on and off (using T₅₇,T₅₄) and can be connected to produce a positive or negative goingwaveform at output terminals AC₃ AC₄, depending on whether Q₅₁, Q₅₃ orQ₅₂, Q₅₄ are triggered. In addition, the only mechanical switches usedare S₁₀, S₁₁.

When switch S₁₁ is released, after switch S₁₁ has been held for 20seconds, pins 4, 5 go low, and after 12 milliseconds, pin 2 goes highand the AC signal at the inputs AC₁, AC₂ is again connected to theoutputs AC₃, AC₄.

To switch the dimmer (and hence the lamp) off, both buttons are pushedsimultaneously, causing all pins to go low, as previously described.

FIG. 8 may be depicted more generally as shown in FIG. 9. Inputterminals AC₁, AC₂ are connected via a selectable switch 80 to inputterminals AC₃, AC₄. Terminals AC₁, AC₂ are also connected via on/offbridge 82 to switch 80 and hence to terminals AC₃, AC₄. The bridge 82and switch 80 are controlled by control circuit 84 which is in turncontrolled by any desired inputs, e.g. switches S₁₀, S₁₁. In FIG. 9, thebridge 82 may be the FIG. 8 bridge comprising thyristors T₅₄, T₅₇ anddiodes D₅₂, D₅₄ (so that the bridge can be switched on or off bytriggering T₅₄, T₅₇), while switch 80 may be triacs T₅₅, T₅₆ andthyristors Q₅₁, Q₅₃, Q₅₂, Q₅₄, which either connect terminals AC₁, AC₂,directly to AC₃, AC₄, or make the connection through a positive ornegative orientation of bridge 82. Control circuit 84 may beoptocouplers OK₁ to OK₈, and control transistors T₅₁, T₅₂, T₅₃, T₅₈, andmicrocontroller 70.

In the embodiments described above, the half cycles of the powerwaveform (negative going as shown in FIG. 3b or positive going as shownin FIG. 3a) have been used for signalling and hence control, but asalways, without disturbing the RMS value of each half cycle of the powerwaveform. While the RMS value of the voltage may vary depending onfluctuations in the supply voltage from the mains, such fluctuationswill not affect the operation of the dimmer since they have little or noinfluence on detection of the sequence of half cycles which are used forsignalling and control. In addition, the method described does notintroduce harmonic distortion into the power waveform, nor does itaffect the power factor. As mentioned, the method is transparent to theload, which treats the sequence of half cycles as if it were anunmodified AC waveform.

It will be realized, however, that other methods can be used forsignalling which have all or substantially all of the advantages of thesystem described above. For example, as shown in FIG. 10, the powerwaveform can be rectified to provide a sequence of positive going halfcycles 86 (which can be considered as "ones") and negative going halfcycles 88 (which can be considered as "zeros"). Sequences such as thatshown in FIG. 10 can readily be produced by the circuit of FIG. 9, usingan appropriate control circuit 84. To produce the FIG. 10 waveforms,control circuit 84 may be of the form shown and described in FIG. 8, butwith microcontroller 70 replaced by a different and suitably programmedmicrocontroller having as inputs either switches S₁₀, S₁₁, or any otherdesired inputs. Again, each half cycle of the FIG. 10 waveform has thesame RMS value as does a half cycle of the unmodified AC waveform.

When a signal of the form shown in FIG. 10 is used to power a resistiveload such as an incandescent lamp, the lamp will again treat such signalas being a conventional power signal, the RMS value of which has notbeen changed. When the load includes an input full wave rectifier, asdoes a gas discharge lamp (as shown at 54 in FIG. 6b), the input fullwave rectifier simply rectifies the waveform shown in FIG. 10 and is notaffected by the coding.

The FIG. 10 waveform can be decoded by any appropriate decoder 16. Thedecoder can include a microprocessor programmed to detect any desiredsequence of positive and negative half cycles and to output a controlsignal of appropriate form to the dimming interface 18 or to any otherload controlled by the system. If desired for the FIG. 10 waveform, thecoding can be arranged so that the code to be acted on is either exactlytwo positive half cycles or two negative cycles. If there are more orless than two consecutive positive or negative half cycles, the decoder16 would treat that part of the waveform as uncoded. This will ensurethat conventional AC waveforms, and full wave rectified waveforms, donot affect the decoder.

If desired, a single dimmer switch can be used to control more than onelamp or load. This can be accomplished by using the arrangement of FIG.11, which corresponds to that of FIG. 9 but has two sets of useroperated switches or buttons S₁₀, S₁₁ and S₁₂, S₁₃. Terminals AC₃, AC₄are connected through a common set of wires 90 to two decoders 16A, 16Bwhich in turn are connected to respective dimming interfaces or loadcontrol circuits 18A, 18B, which in turn are connected to loads (usuallylamps) 28A, 28B. One set of switches S₁₀, S₁₁ causes bridge 82 andswitch 80 to produce output waveform cycle sequences of half cycleswhich are decoded by decoder 16A to control only load control circuit18A which controls load 28A. The other set of switches S₁₂, S₁₃ does thesame for load 28B. In all cases, power for both loads is conducted alongthe common wires 90 and may be unmodified AC or may be the particularsequences of half cycles which are also used for control. If desired,switches S₁₀ to S₁₃ may take any user-friendly form, e.g. two slideswitches, or a single slide switch operated in one direction to operateload 28A and in the other direction to operate load 28B (if the loadsare intended to operate only alternatively), with appropriateprogramming. Similarly, three or more loads can be powered andcontrolled along a common set of wires, by using sufficient selectedsequences of half cycles as codes, for control, and for power. In allcases, the RMS value of each half cycle will be substantially the sameas for corresponding half cycles of the unmodified AC waveform.

If desired, the sequences of half cycles used for coding (and for power)can include a combination of the sequences shown in FIGS. 3a to 3d andFIG. 10.

If the load is relatively small (e.g. a compact fluorescent lamp), thenother methods can be used to code using half cycles of the powerwaveform. For example, reference is made to FIG. 12, which is a simpleblock diagram corresponding to FIG. 2, and in which correspondingreference numerals indicate corresponding parts. FIG. 12 differs fromFIG. 2 only in that capacitors C₁₀₀, C₁₀₁ have been placed across theoutputs of bridges BR₁, BR₂ and are switchable in and out of the circuitby electronic switches SW₁₀₀, SW₁₀₁ (which can be operated by amicrocontroller, not shown, to switch the capacitors into the circuitfor a brief portion of each cycle or half cycle at any selected time).If the capacitors C₁₀₀, C₁₀₁ are sufficiently large relative to theload, then they will affect the shape of the waveform (acting in effectas filter capacitors), but without substantially affecting the RMS valueof the signal, and therefore without affecting the operation of the lampor other load. The change in waveform can be detected by anyconventional arrangement and can be used as additional information, e.g.to control a single load in the manner previously described, or todetermine what load to control if power is being supplied through thedimmer or control device to more than one load. It is of courseimportant in all cases, and particularly in the circuit shown in FIG.12, to ensure that the total harmonic distortion (in the transmitted ACwaveform) does not exceed a selected limit, preferably 20% and morepreferably 10%. In addition, the method used for signalling should notreduce the power factor of the transmitted waveform (at terminals AC₃,A₄) below 90% as compared with the power factor of the input waveform(at terminals AC₁, AC₂). Further, it is important that high frequencycomponents not be used for signalling (e.g. no frequency componentsabove about 100 KHz). However, desirably, each half cycle of the signalis left substantially unchanged in shape (or is changed such that totalharmonic distortion as mentioned is less than about 20%, preferably lessthan 10%), but the arrangement of the half cycles of the power signal isused for signalling (e.g. full wave positively or negatively rectifiedas shown in FIG. 3, or coded as shown in FIG. 10). This arrangement doesnot affect the power factor, does not introduce any harmonic distortion,does not change the RMS value of the power signal, does not require anyadditional wiring, and is relatively simple to use in practice.

If desired, instead of using the capacitors shown in FIG. 12, inductorsL₁, L₂ can be used as shown in FIG. 13 to change the waveform to alimited extent to introduce additional signalling capabilities. Again,switches S₁₀₂, S₁₀₃ are electronically controlled to switch theinductors in and out of each half cycle as desired, for an appropriatelength of time, so as to change the waveform sufficiently for detectionbut not so much as to introduce more than the amount of harmonicdistortion referred to above. Again, the FIG. 13 arrangement will beused only where the values of inductors L₁, L₂ can be relatively largerelative to the load.

In addition to providing dimming control for lighting ballasts andlamps, the present invention may also be used to control generalhousehold devices containing a front-end full wave bridge rectifier,such as burglar alarms, smoke alarms, and some heaters, air conditioningunits, refrigerators, etc. As previously discussed, the devicescontrolled are either essentially resistive loads or have an internalbridge rectifier to full wave rectify the AC waveform. Since thisinternal bridge rectifier will also rectify a full wave positivelyrectified AC signal or a full wave negatively rectified AC signal into afull wave (usually positively) rectified AC signal, it is of noconsequence to provide such a device with a full wave positively ornegatively rectified AC signal or coded AC signal in place of AC source20.

In this way, such household devices can be controlled by a deviceinterface comprising any logic circuit which can differentiate betweenthe signals described and which controls the device accordingly. Controlof such devices may be achieved using a stand-alone computer or otherremote control device connected to a wall outlet and does not requirethe installation of special switches or the running of separatecommunication wires to the device.

Since dimmer 10 may not be directly employed with AC devices thatutilize transformers (a similar restriction exists for traditionaldimming circuits), it is desirable to install a simple conventionalelectrical fuse circuit at the input of such devices. This fuse circuitwill check the impedance of the device in a conventional manner and willdisable the dimmer 10 if the impedance is low (i.e. if a transformer issensed).

Finally, although the preferred embodiment has been described inconnection with a two phase 60 Hz power line, the principle of thepresent invention can be applied to multiple-phase configurations, e.g.three phase configurations.

As will be apparent to persons skilled in the art, various modificationsand adaptations of the structure described above are possible withoutdeparture from the present invention, the scope of which is defined inthe appended claims.

I claim:
 1. A control circuit for controlling an electrical load havinga load input, said control circuit comprising:(a) a power input forreceiving an input AC waveform having a selected RMS value, (b) arectifying circuit coupled to said input for producing at a power outputone of a plurality of output waveforms from said AC input waveform, eachoutput waveform having an RMS value substantially the same as saidselected RMS value, (c) a controller coupled to said rectifying circuitand operative to cause said rectifying circuit to produce at said poweroutput a selected one of said output waveforms, (d) said load inputbeing adapted to be coupled to said power output for receiving saidselected output waveform so that said selected output waveform providespower to said load, (e) and a decoder control circuit adapted to becoupled to said power output and to said load and responsive to theselected output waveform from said rectifying circuit for controllingsaid load.
 2. A control circuit according to claim 1 wherein said outputwaveforms include at least some positive half cycles of said inputwaveform and at least some negative half cycles of said input waveform.3. A control circuit according to claim 1 wherein said output waveformsinclude said input waveform, said input waveform full wave positivelyrectified, and said input waveform full wave negatively rectified.
 4. Acontrol circuit according to claim 1 wherein said output waveformsinclude a plurality of half cycles of said input waveform positivelyrectified and a plurality of half cycles of said input waveformsnegatively rectified, the sequence of positive and negative half cyclesin said output waveform comprising a code.
 5. A control circuitaccording to claim 3 wherein said output waveforms include a pluralityof half cycles of said input waveform positively rectified and aplurality of half cycles of said input waveforms negatively rectified,the sequence of positive and negative half cycles in said outputwaveform comprising a code.
 6. A control circuit according to claim 4 or5 wherein said sequence comprises at least two sequential positive halfcycles separated from the remainder of said sequences by at least onenegative half cycle, and two sequential negative half cycles separatedfrom the remainder of said sequences by at least one positive halfcycle.
 7. A control circuit according to any of claims 1 to 5 whereineach of said output waveforms has total harmonic distortion of less thanor equal to 20%.
 8. A control circuit according to any of claims 1 to 5wherein the power factor of each of said output waveforms differs fromthe power factor of said input waveform by less than 10%.
 9. A controlcircuit according to claim 1 wherein said rectifying circuit comprises afull wave bridge.
 10. A control circuit according to claim 9 whereinsaid rectifying circuit includes a switch circuit responsive to saidcontroller for selectively coupling said power input to said poweroutput, or for connecting said bridge between said power input and saidpower output to provide a first output waveform which comprises saidinput waveform positively rectified, or for connecting said bridgebetween said input and output to provide a second output waveform whichcomprises said input waveform negatively rectified.
 11. A controlcircuit according to claim 10 wherein said first output waveform is fullwave positively rectified and said second output waveform is full wavenegatively rectified.
 12. A control circuit according to claim 11wherein said switch circuit comprises at least one manually operatedswitch coupled to said controller for controlling said switch circuit sothat said input waveform is normally connected to said power output oris normally disconnected from said output, and for momentarilyconnecting either said full wave positively or said full wave negativelyrectified waveform to said power output.
 13. A control circuit accordingto claim 10 wherein said controller includes a microcontroller coupledto said bridge and to said switch circuit for controlling the sequenceand polarity of the half cycles of the output waveform at said poweroutput.
 14. A control circuit according to claim 9 wherein saidrectifying circuit comprises two full wave bridges, and a switchingcircuit responsive to said controller for connecting one or the other ofsaid full wave bridges between said power input and said power output.15. A control circuit according to claim 1 wherein said load is anelectrical light.
 16. A control circuit according to claim 15 whereinsaid light is a resistance device.
 17. A control circuit according toclaim 15 wherein said light is a gas discharge device.
 18. A controlcircuit according to claim 1 wherein said decoder control circuitincludes a decoder coupled to said power output for decoding the outputwaveforms at said power output, for producing a decoder signal, and aload control circuit coupled to said decoder and to said load andresponsive to said decoder signal for controlling said load.
 19. Acontrol circuit according to claim 18 wherein said load control circuitincludes a lead for applying power to said load.
 20. A control circuitaccording to claim 18 wherein said load is connected to said poweroutput and includes a further control circuit connected to said loadcontrol circuit and responsive to the operation thereof for controllingsaid load.
 21. A method of controlling an electrical load at a firstlocation connected by power wires to an AC source at a second location,said AC source providing an AC waveform having a selected RMS value,said method comprising:(a) controlling said AC waveform at said secondlocation to produce a set of power waveforms each having an RMS valuesubstantially equal to said selected RMS value, (b) selectivelytransmitting one of said set of power waveforms from said secondlocation over said power wires to said electrical load to provide powerto said load, (c) at said first location, decoding said power waveformsand controlling said electrical device in accordance therewith.
 22. Amethod according to claim 21 wherein said set of power waveformscomprises a first power waveform consisting of said AC waveform, asecond power waveform consisting of the absence of said AC waveform, athird power waveform comprising at least a portion of said AC waveformrectified positively, and a fourth power waveform comprising at least aportion of said AC waveform rectified negatively.
 23. A method accordingto claim 22, wherein said electrical load is a lamp.
 24. A methodaccording to claim 23, including using said third and fourth powerwaveforms to increase and decrease the brightness of said lamp.
 25. Amethod according to claim 21 including providing a dimmer circuit atsaid second location, said dimmer circuit including a switch, andoperating said switch to provide said respective power waveforms.
 26. Amethod according to claim 22 wherein said third and fourth powerwaveforms are full wave rectified.